It is well known that t-butyl (meth)acrylate is not easily synthesized by a dehydration esterification reaction between a carboxylic acid and an alcohol, which is a general synthesizing method of an ester, or by an ester interchange reaction between a (meth)acrylate and t-butyl alcohol. This is because, in the case of the dehydration esterification reaction, t-butyl alcohol, which is a tertiary alcohol, is easily decomposed in the presence of a strong acid, which is a common catalyst, and isobutylene produced is removed from the reaction system simultaneously with the dehydration and hence a reaction producing an ester does not proceed. Further, in the case of the ester interchange reaction, a basic catalyst, a metal alkoxide catalyst or the like is an effective catalyst which can suppress decomposition of t-butyl alcohol, however, a formation of t-butyl ester is suppressed because a t-butyl group in an activated t-butyl alcohol stereochemically obstructs reactivity of a hydroxyl group.
Consequently, it has been conventionally known that an addition reaction between (meth)acrylic acid and isobutylene is effective for a synthesis of t-butyl (meth)acrylate. However, this method is unfavorable in view of cost of raw materials because isobutylene is relatively expensive. As an economical and advantageous method for producing t-butyl (meth)acrylate by reducing the cost of raw materials through suppressing side reactions, a method of suppressing conversion (Patent Document 1) and a method of lowering a reaction temperature (Patent Document 2) are listed. However, expensive isobutylene is still used in these methods, and besides, a countermeasure for a pressurized gas is necessary because isobutylene, which is a raw material, is in many cases used in a pressurized gas state, and hence these methods are economically unfavorable.
On the other hand, various methods for producing isobutylene from t-butyl alcohol, which is an inexpensive raw material, have been known.
For example, a dehydration decomposition reaction of t-butyl alcohol easily occurs to produce isobutylene by using a strongly acidic catalyst in a liquid-phase system and heating the liquid-phase system (Patent Documents 3, 4 and 5).
Further, it has also been well known that a dehydration decomposition reaction of t-butyl alcohol easily occurs to produce isobutylene by contacting gaseous t-butyl alcohol to a solid acid catalyst such as a solid phosphoric acid, an activated alumina or silica-alumina at a high temperature in a gas-phase system (Patent Documents 6 and 7).
However, in any of these methods, vapor pressures of water to be produced, isobutylene dimer, which is a main product by side reactions, and t-butyl alcohol, which is a raw material, are relatively high at a temperature at which the dehydration decomposition reaction is performed effectively, and hence these materials mix in a target isobutylene when isobutylene produced is taken out of the dehydration reaction system as a gas.
Consequently, when the isobutylene gas produced is directly introduced into a step of an addition reaction with (meth)acrylic acid, isobutylene is hydrated again to change into t-butyl alcohol by moisture contained in the isobutylene at an equivalent amount or more. In this case, there has been a problem which is specific in this system and has to be improved, namely, the problem that productivity of a (meth)acrylate reduces because it is very difficult to advance the dehydration esterification reaction between t-butyl alcohol and (meth)acrylic acid as mentioned above.
On the other hand, in the case that isobutylene is isolated in high purity, conduction of a high degree distillation operation or a condensation-separation operation which uses an expensive refrigeration energy is necessary to separate water to be produced and unreacted t-butyl alcohol, and moreover, a compressor or a cooling system is used in order to collect isobutylene as a liquefied gas, and consequently, installation cost and energy cost become very large and hence this is economically unfavorable.
Patent Document 1: Japanese Patent Application Laid-Open No. Sho 63-135,352
Patent Document 2: Japanese Patent Application Laid-Open No. Sho 62-63,544
Patent Document 3: U.S. Pat. No. 4,012,456
Patent Document 4: Japanese Patent Application Laid-Open No. Sho 54-135,710
Patent Document 5: Japanese Patent Application Laid-Open No. Sho 54-138,506
Patent Document 6: U.S. Pat. No. 4,036,905
Patent Document 7: Japanese Patent Application Laid-Open No. Sho 47-13,250